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As a temporary mechanism enabling the support of generic classes, the GNU
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[val,ref] proto, where proto is the name of the class being
generated. Container classes like dictionaries and maps that require
two types may be specified via genclass -2 keytype [val, ref],
basetype [val, ref] proto, where the key type is specified first and
the contents type second. The resulting classnames and filenames are
generated by prepending the specified type names to the prototype names,
and separating the filename parts with dots. For example,
genclass int val List generates class intList residing in
files `int.List.h' and `int.List.cc'. genclass -2 String
ref int val VHMap generates (the awkward, but unavoidable) class name
StringintVHMap. Of course, programmers may use typedef or
simple editing to create more appropriate names. The existence of dot
seperators in file names allows the use of GNU make to help automate
configuration and recompilation. An example Makefile exploiting such
capabilities may be found in the `libg++/proto-kit' directory.

The genclass utility operates via simple text substitution using
sed. All occurrences of the pseudo-types <T> and <C>
(if there are two types) are replaced with the indicated type, and
occurrences of <T&> and <C&> are replaced by just the types,
if val is specified, or types followed by "&" if ref is
specified.

Programmers will frequently need to edit the `.h' file in order to
insert additional #include directives or other modifications. A
simple utility, `prepend-header' to prepend other `.h' files
to generated files is provided in the distribution.

One dubious virtue of the prototyping mechanism is that, because sources files,
not archived library classes, are generated, it is relatively simple for
programmers to modify container classes in the common case where slight
variations of standard container classes are required.

It is often a good idea for programmers to archive (via ar)
generated classes into `.a' files so that only those class
functions actually used in a given application will be loaded.
The test subdirectory of the distribution shows an example of this.

Because of #pragma interface directives, the `.cc' files
should be compiled with -O or -DUSE_LIBGXX_INLINES
enabled.

Many container classes require specifications over and above the base
class type. For example, classes that maintain some kind of ordering of
elements require specification of a comparison function upon which to
base the ordering. This is accomplished via a prototype file
`defs.hP' that contains macros for these functions. While these
macros default to perform reasonable actions, they can and should be
changed in particular cases. Most prototypes require only one or a few
of these. No harm is done if unused macros are defined to perform
nonsensical actions. The macros are:

All object containers must perform either a X::X(X&) (or
X::X() followed by X::operator =(X&)) to copy objects into
containers. (The latter form is used for containers built from C++
arrays, like VHSets). When containers are destroyed, they invoke
X::~X(). Any objects used in containers must have well behaved
constructors and destructors. If you want to create containers that
merely reference (point to) objects that reside elsewhere, and are not
copied or destroyed inside the container, you must use containers
of pointers, not containers of objects.

All prototypes are designed to generate HOMOGENOUS container
classes. There is no universally applicable method in C++ to support
heterogenous object collections with elements of various subclasses of
some specified base class. The only way to get heterogenous structures
is to use collections of pointers-to-objects, not collections of objects
(which also requires you to take responsibility for managing storage for
the objects pointed to yourself).

For example, the following usage illustrates a commonly encountered
danger in trying to use container classes for heterogenous structures:

At the line flagged with `(CHOP!)', a Base::Base(Base&) is
called inside Set::add(Base&)---notDerived::Derived(Derived&). Actually, in VHSet, a
Base::operator =(Base&), is used instead to place the element in
an array slot, but with the same effect. So only the Base part is
copied as a VHSet element (a so-called chopped-copy). In this
case, it has an x part, but no y part; and a Base, not
Derived, vtable. Objects formed via chopped copies are rarely
sensible.

Your first decision is what storage/usage strategy to use. There are
several reasonable alternatives here: You might create an "object
collection" of Persons, a "pointer collection" of
pointers-to-Persons, or even a simple String map, housing either copies
of pointers to the names of Persons, since other fields are unused for
purposes of the Map. In an object collection, instances of class Person
"live" inside the Map, while in a pointer collection, the instances
live elsewhere. Also, as above, if instances of subclasses of Person are
to be used inside the Map, you must use pointers. In a String Map, the
same difference holds, but now only for the name fields. Any of these
choices might make sense in particular applications.

The second choice is the Map implementation strategy. Either a tree
or a hash table might make sense. Suppose you want an AVL tree Map.
There are two things to now check. First, as an object collection,
the AVLMap requires that the elsement class contain an X(X&)
constructor. In C++, if you don't specify such a constructor, one
is constructed for you, but it is a very good idea to always do this
yourself, to avoid surprises. In this example, you'd use something like

Also, an AVLMap requires a comparison function for elements in order
to maintain order. Rather than requiring you to write a particular
comparison function, a `defs' file is consulted to determine how to
compare items. You must create and edit such a file.

Before creating `Person.defs.h', you must first make one additional
decision. Should the Map member functions like m.contains(p)
take arguments (p) by reference (i.e., typed as
int Map::contains(const Person& p) or by value (i.e., typed as
int Map::contains(const Person p). Generally, for user-defined
classes, you want to pass by reference, and for builtins and pointers,
to pass by value. SO you should pick by-reference.

You can now create `Person.defs.h' via genclass Person ref defs.
This creates a simple skeleton that you must edit. First, add
#include "Person.h" to the top. Second, edit the <T>CMP(a,b)
macro to compare on name, via

#define <T>CMP(a, b) ( compare(a.name(), b.name()) )

which invokes the int compare(const String&, const String&)
function from `String.h'. Of course, you could define this in any
other way as well. In fact, the default versions in the skeleton turn
out to be OK (albeit inefficient) in this particular example.

You may also want to create file `SSN.defs.h'. Here, choosing
call-by-value makes sense, and since no other capabilities (like
comparison functions) of the SSNs are used (and the defaults are OK
anyway), you'd type

genclass SSN val defs

and then edit to place #include "SSN.h" at the top.

Finally, you can generate the classes. First, generate the base
class for Maps via

genclass -2 Person ref SSN val Map

This generates only the abstract class, not the implementation, in file
`Person.SSN.Map.h' and `Person.SSN.Map.cc'. To create the
AVL implementation, type

genclass -2 Person ref SSN val AVLMap

This creates the class PersonSSNAVLMap, in
`Person.SSN.AVLMap.h' and `Person.SSN.AVLMap.cc'.

To use the AVL implementation, compile the two generated `.cc' files, and
specify `#include "Person.SSN.AVLMap.h"' in the application program.
All other files are included in the right ways automatically.

One last consideration, peculiar to Maps, is to pick a reasonable
default contents when declaring an AVLMap. Zero might be appropriate
here, so you might declare a Map,

PersonSSNAVLMap m((SSN)0);

Suppose you wanted a VHMap instead of an AVLMap Besides
generating different implementations, there are two differences in
how you should prepare the `defs' file. First, because a VHMap
uses a C++ array internally, and because C++ array slots are initialized
differently than single elements, you must ensure that class Person
contains (1) a no-argument constructor, and (2) an assignment operator.
You could arrange this via

Since the hashpjw function from `builtin.h' is
appropriate here. Changing the default capacity to a value
expected to exceed the actual capacity helps to avoid
"hidden" inefficiencies when a new VHMap is created without
overriding the default, which is all too easy to do.

Otherwise, everything is the same as above, substituting
VHMap for AVLMap.

One of the first goals of the GNU C++ library is to enrich the kinds of
basic classes that may be considered as (nearly) "built into" C++. A good
deal of the inspiration for these efforts is derived from considering
features of other type-rich languages, particularly Common Lisp and Scheme.
The general characteristics of most class and friend operators and
functions supported by these classes has been heavily influenced
by such languages.

Four of these types, Strings, Integers, BitSets, and BitStrings (as well as
associated and/or derived classes) require representations suitable for
managing variable-sized objects on the free-store. The basic technique used
for all of these is the same, although various details necessarily differ
from class to class.

The general strategy for representing such objects is to create chunks of
memory that include both header information (e.g., the size of the object),
as well as the variable-size data (an array of some sort) at the end
of the chunk. Generally the maximum size of an object is limited to
something less than all of addressable memory, as a safeguard. The minimum
size is also limited so as not to waste allocations expanding very small
chunks. Internally, chunks are allocated in blocks well-tuned to the
performance of the new operator.

Class elements themselves are merely pointers to these chunks.
Most class operations are performed via inline "translation"
functions that perform the required operation on the corresponding
representation. However, constructors and assignments operate by
copying entire representations, not just pointers.

No attempt is made to control temporary creation in expressions
and functions involving these classes. Users of previous versions
of the classes will note the disappearance of both "Tmp" classes
and reference counting. These were dropped because, while they
did improve performance in some cases, they obscure class
mechanics, lead programmers into the false belief that they need not
worry about such things, and occasionally have paradoxical behavior.

These variable-sized object classes are integrated as well as possible
into C++. Most such classes possess converters that allow automatic
coercion both from and to builtin basic types. (e.g., char* to and from
String, long int to and from Integer, etc.). There are pro's and con's
to circular converters, since they can sometimes lead to the conversion
from a builtin type through to a class function and back to a builtin
type without any special attention on the part of the programmer, both
for better and worse.

Most of these classes also provide special-case operators and functions
mixing basic with class types, as a way to avoid constructors in cases
where the operations do not rely on anything special about the
representations. For example, there is a special case concatenation
operator for a String concatenated with a char, since building the
result does not rely on anything about the String header. Again, there
are arguments both for and against this approach. Supporting these cases
adds a non-trivial degree of (mainly inline) function proliferation, but
results in more efficient operations. Efficiency wins out over parsimony
here, as part of the goal to produce classes that provide sufficient
functionality and efficiency so that programmers are not tempted to try
to manipulate or bypass the underlying representations.

The fact that C++ allows operators to be overloaded for user-defined
classes can make programming with library classes like Integer,
String, and so on very convenient. However, it is worth
becoming familiar with some of the inherent limitations and problems
associated with such operators.

Many operators are constructive, i.e., create a new object
based on some function of some arguments. Sometimes the creation
of such objects is wasteful. Most library classes supporting
expressions contain facilities that help you avoid such waste.

For example, for Integer a, b, c; ...; c = a + b + a;, the
plus operator is called to sum a and b, creating a new temporary object
as its result. This temporary is then added with a, creating another
temporary, which is finally copied into c, and the temporaries are then
deleted. In other words, this code might have an effect similar to
Integer a, b, c; ...; Integer t1(a); t1 += b; Integer t2(t1);
t2 += a; c = t2;.

For small objects, simple operators, and/or non-time/space critical
programs, creation of temporaries is not a big problem. However, often,
when fine-tuning a program, it may be a good idea to rewrite such
code in a less pleasant, but more efficient manner.

For builtin types like ints, and floats, C and C++ compilers already
know how to optimize such expressions to reduce the need for
temporaries. Unfortunately, this is not true for C++ user defined
types, for the simple (but very annoying, in this context) reason that
nothing at all is guaranteed about the semantics of overloaded operators
and their interrelations. For example, if the above expression just
involved ints, not Integers, a compiler might internally convert the
statement into something like c += a; c += b; c+= a; , or
perhaps something even more clever. But since C++ does not know that
Integer operator += has any relation to Integer operator +, A C++
compiler cannot do this kind of expression optimization itself.

In many cases, you can avoid construction of temporaries simply by
using the assignment versions of operators whenever possible, since
these versions create no temporaries. However, for maximum flexibility,
most classes provide a set of "embedded assembly code" procedures
that you can use to fully control time, space, and evaluation strategies.
Most of these procedures are "three-address" procedures that take
two const source arguments, and a destination argument. The
procedures perform the appropriate actions, placing the results in
the destination (which is may involve overwriting old contents). These
procedures are designed to be fast and robust. In particular, aliasing
is always handled correctly, so that, for example
add(x, x, x); is perfectly OK. (The names of these procedures
are listed along with the classes.)

This function, when called (as in a = f(a); ) demonstrates a
similar kind of wasted copy. The returned value r must be copied
out of the function before it can be used by the caller. In GNU
C++, there is an alternative via the use of named return values.
Named return values allow you to manipulate the returned object
directly, rather than requiring you to create a local inside
a function and then copy it out as the returned value. In this
example, this can be done via
Integer f(const Integer& a) return r(a) { r += a; return; }

A final guideline: The overloaded operators are very convenient, and
much clearer to use than procedural code. It is almost always a good
idea to make it right, then make it fast, by translating
expression code into procedural code after it is known to be correct.

Many useful classes operate as containers of elements. Techniques for
accessing these elements from a container differ from class to class.
In the GNU C++ library, access methods have been partially standardized
across different classes via the use of pseudo-indexes called
Pixes. A Pix acts in some ways like an index, and in some
ways like a pointer. (Their underlying representations are just
void* pointers). A Pix is a kind of "key" that is
translated into an element access by the class. In virtually all cases,
Pixes are pointers to some kind internal storage cells. The
containers use these pointers to extract items.

Pixes support traversal and inspection of elements in a
collection using analogs of array indexing. However, they are
pointer-like in that 0 is treated as an invalid Pix, and
unsafe insofar as programmers can attempt to access nonexistent elements
via dangling or otherwise invalid Pixes without first checking
for their validity.

In general it is a very bad idea to perform traversals in the the midst
of destructive modifications to containers.

Typical applications might include code using the idiom

for (Pix i = a.first(); i != 0; a.next(i)) use(a(i));

for some container a and function use.

Classes supporting the use of Pixes always contain the following
methods, assuming a container a of element types of Base.

Pix i = a.first()

Set i to index the first element of a or 0 if a is empty.

a.next(i)

advance i to the next element of a or 0 if there is no next element;

Base x = a(i); a(i) = x;

a(i) returns a reference to the element indexed by i.

int present = a.owns(i)

returns true if Pix i is a valid Pix in a. This is often a
relatively slow operation, since the collection must usually
traverse through elements to see if any correspond to the Pix.

Some container classes also support backwards traversal via

Pix i = a.last()

Set i to the last element of a or 0 if a is empty.

a.prev(i)

sets i to the previous element in a, or 0 if there is none.

Collections supporting elements with an equality operation possess

Pix j = a.seek(x)

sets j to the index of the first occurrence of x, or 0 if x is
not contained in a.

Bag classes possess

Pix j = a.seek(x, Pix from = 0)

sets j to the index of the next occurrence of x following i,
or 0 if x is not contained in a. If i == 0, the first occurrence
is returned.

Set, Bag, and PQ classes possess

Pix j = a.add(x) (or a.enq(x) for priority queues)

add x to the collection, returning its Pix. The Pix of an item
can change in collections where further additions and deletions
involve the actual movement of elements (currently in OXPSet,
OXPBag, XPPQ, VOHSet), but in all other cases, an item's Pix may
be considered a permanent key to its location.

The following files are provided so that C++ programmers may
invoke common C library and system calls. The names and contents
of these files are subject to change in order to be compatible
with the forthcoming GNU C library. Other files, not listed
here, are simply C++-compatible interfaces to corresponding C
library files.

`values.h'

A collection of constants defining the numbers of bits in builtin
types, minimum and maximum values, and the like. Most names are
the same as those found in `values.h' found on Sun systems.

`std.h'

A collection of common system calls and `libc.a' functions.
Only those functions that can be declared without introducing
new type definitions (socket structures, for example) are
provided. Common char* functions (like strcmp) are among
the declarations. All functions are declared along with their
library names, so that they may be safely overloaded.

`string.h'

This file merely includes `<std.h>', where string function
prototypes are declared. This is a workaround for the fact that
system `string.h' and `strings.h' files often differ
in contents.

`osfcn.h'

This file merely includes `<std.h>', where system function
prototypes are declared.

`libc.h'

This file merely includes `<std.h>', where C library function
prototypes are declared.

`math.h'

A collection of prototypes for functions usually found in
libm.a, plus some #defined constants that appear to be
consistent with those provided in the AT&T version. The value
of HUGE should be checked before using. Declarations of
all common math functions are preceded with overload
declarations, since these are commonly overloaded.

`stdio.h'

Declaration of FILE (_iobuf), common macros (like
getc), and function prototypes for `libc.a'
functions that operate on FILE*'s. The value
BUFSIZ and the declaration of _iobuf should be
checked before using.

`assert.h'

C++ versions of assert macros.

`generic.h'

String concatenation macros useful in creating generic classes.
They are similar in function to the AT&T CC versions.

Libg++ contains versions of malloc, free, realloc that were
designed to be well-tuned to C++ applications. The source file
`malloc.c' contains some design and implementation details.
Here are the major user-visible differences from most system
malloc routines:

These routines overwrite storage of freed space. This
means that it is never permissible to use a delete'd
object in any way. Doing so will either result in trapped
fatal errors or random aborts within malloc, free, or realloc.

The routines tend to perform well when a large number
of objects of the same size are allocated and freed. You
may find that it is not worth it to create your
own special allocation schemes in such cases.

The library sets top-level operator new() to call malloc and
operator delete() to call free. Of course, you may override these
definitions in C++ programs by creating your own operators that will
take precedence over the library versions. However, if you do so, be
sure to define bothoperator new() and operator
delete().

These routines do not support the odd convention, maintained by
some versions of malloc, that you may call realloc with a pointer
that has been free'd.

The routines automatically perform simple checks on free'd
pointers that can often determine whether users have accidentally
written beyond the boundaries of allocated space, resulting in a fatal
error.

The function malloc_usable_size(void* p) returns the number of
bytes actually allocated for p. For a valid pointer (i.e., one
that has been malloc'd or realloc'd but not yet
free'd) this will return a number greater than or equal to the
requested size, else it will normally return 0. Unfortunately, a
non-zero return can not be an absolutely perfect indication of lack of
error. If a chunk has been free'd but then re-allocated for a
different purpose somewhere elsewhere, then malloc_usable_size
will return non-zero. Despite this, the function can be very valuable
for performing run-time consistency checks.

malloc requires 8 bytes of overhead per allocated chunk, plus a
mmaximum alignment adjustment of 8 bytes. The number of bytes of usable
space is exactly as requested, rounded to the nearest 8 byte boundary.

The routines do not contain any synchronization support for
multiprocessing. If you perform global allocation on a shared
memory multiprocessor, you should disable compilation and use
of libg++ malloc in the distribution `Makefile' and use your
system version of malloc.

The iostream classes implement most of the features of AT&T
version 2.0 iostream library classes, and most of the features
of the ANSI X3J16 library draft (which is based on the AT&T design).
These classes are available in libg++ for convenience and for
compatibility with older releases; however, since the iostream classes
are licensed under less stringent terms than libg++, they are now
also available in a separate library called libio---and
documented in a separate manual, corresponding to that library.

WARNING: This chapter describes classes that are obsolete.
These classes are normally not available when libg++
is installed normally. The sources are currently included
in the distribution, and you can configure libg++ to use
these classes instead of the new iostream classes.
This is only a temporary measure; you should convert your
code to use iostreams as soon as possible. The iostream
classes provide some compatibility support, but it is
very incomplete (there is no longer a File class).

The File class supports basic IO on Unix files. Operations are
based on common C stdio library functions.

File serves as the base class for istreams, ostreams, and other
derived classes. It contains the interface between the Unix stdio file
library and these more structured classes. Most operations are implemented
as simple calls to stdio functions. File class operations are also fully
compatible with raw system file reads and writes (like the system
read and lseek calls) when buffering is disabled (see below).
The FILE* stdio file pointer is, however maintained as protected.
Classes derived from File may only use the IO operations provided by File,
which encompass essentially all stdio capabilities.

The class contains four general kinds of functions: methods for binding
Files to physical Unix files, basic IO methods, file and buffer
control methods, and methods for maintaining logical and physical file
status.

If a file name is provided in a constructor or open, it is
maintained as class variable nm and is accessible
via name. If no name is provided, then nm remains
null, except that Files bound to the default files stdin,
stdout, and stderr are automatically given the names
(stdin), (stdout), (stderr) respectively.
The function setname may be used to change the
internal name of the File. This does not change the name
of the physical file bound to the File.
The member function close closes a file. The
~File destructor closes a file if it is open, except
that stdin, stdout, and stderr are flushed but left open for
the system to close on program exit since some systems may
require this, and on others it does not matter. remove
closes the file, and then deletes it if possible by calling the
system function to delete the file with the name provided in
the nm field.

setbuf is mainly useful to turn off buffering in cases
where nonsequential binary IO is being performed. raw is a
synonym for setbuf(_IONBF). After a f.raw(), using
the stdio functions instead of the system read, write,
etc., calls entails very little overhead. Moreover, these become
fully compatible with intermixed system calls (e.g.,
lseek(f.filedesc(), 0, 0)). While intermixing File
and system IO calls is not at all recommended, this technique
does allow the File class to be used in conjunction with
other functions and libraries already set up to operate on file
descriptors. setbuf should be called at most once after a
constructor or open, but before any IO.

A File may be checked for accessibility via
is_open(), which returns true if the File is bound to a
usable physical file, readable(), which returns true if
the File can be read from (opened for reading, and not in a
_fail state), or writable(), which returns true if the
File can be written to.

File operations return their status via two means: failure and
success are represented via the logical state. Also, the
return values of invoked stdio and system functions that
return useful numeric values (not just failure/success flags)
are held in a class variable accessible via iocount.
(This is useful, for example, in determining the number of
items actually read by the read function.)

Like the AT&T i/o-stream classes, but unlike the description in
the Stroustrup book, p238, rdstate() returns the bitwise
OR of _eof, _fail and _bad, not necessarily
distinct values. The functions eof(), fail(),
bad(), and good() can be used to test for each of
these conditions independently.

_fail becomes set for any input operation that could not
read in the desired data, and for other failed operations. As
with all Unix IO, _eof becomes true only when an input
operations fails because of an end of file. Therefore,
_eof is not immediately true after the last successful
read of a file, but only after one final read attempt. Thus, for
input operations, _fail and _eof almost always
become true at the same time. bad is set for unbound
files, and may also be set by applications in order to communicate
input corruption. Conversely, _good is defined as 0 and
is returned by rdstate() if all is well.

The state may be modified via clear(flag), which,
despite its name, sets the corresponding state_value flag.
clear() with no arguments resets the state to _good.
failif(int cond) sets the state to _fail only if
cond is true.

Errors occuring during constructors and file opens also invoke the
function error. error in turn calls a resetable error
handling function pointed to by the non-member global variable
File_error_handler only if a system error has been generated.
Since error cannot tell if the current system error is actually
responsible for a failure, it may at times print out spurious messages.
Three error handlers are provided. The default,
verbose_File_error_handler calls the system function
perror to print the corresponding error message on standard
error, and then returns to the caller. quiet_File_error_handler
does nothing, and simply returns. fatal_File_error_handler
prints the error and then aborts execution. These three handlers, or any
other user-defined error handlers can be selected via the non-member
function set_File_error_handler.

All read and write operations communicate either logical or
physical failure by setting the _fail flag. All further
operations are blocked if the state is in a _fail or_bad
condition. Programmers must explicitly use clear() to
reset the state in order to continue IO processing after
either a logical or physical failure. C programmers who are
unfamiliar with these conventions should note that, unlike
the stdio library, File functions indicate IO success,
status, or failure solely through the state, not via return values of
the functions. The void* operator or rdstate()
may be used to test success. In particular, according to c++
conversion rules, the void* coercion is automatically
applied whenever the File& return value of any File
function is tested in an if or while. Thus,
for example, an easy way to copy all of stdin to stdout until
eof (at which point get fails) or some error is
char c; while(cin.get(c) && cout.put(c));.

The current version of istreams and ostreams differs significantly
from previous versions in order to obtain compatibility with
AT&T 1.2 streams. Most code using previous versions should still
work. However, the following features of File are not
incorporated in streams (they are still present in File):
scan(const char* fmt...), remove(), read(), write(),
setbuf(), raw(). Additionally, the feature of previous streams
that allowed free intermixing of stream and stdio input and output
is no longer guaranteed to always behave as desired.

The Obstack class is a simple rewrite of the C obstack macros and
functions provided in the GNU CC compiler source distribution.

Obstacks provide a simple method of creating and maintaining a string
table, optimized for the very frequent task of building strings
character-by-character, and sometimes keeping them, and sometimes
not. They seem especially useful in any parsing application. One of the
test files demonstrates usage.

A brief summary:

grow

places something on the obstack without committing to wrap
it up as a single entity yet.

finish

wraps up a constructed object as a single entity,
and returns the pointer to its start address.

copy

places things on the obstack, and does wrap them up.
copy is always equivalent to first grow, then finish.

free

deletes something, and anything else put on the obstack since its creation.

The other functions are less commonly needed:

blank

is like grow, except it just grows the space by size units
without placing anything into this space

alloc

is like blank, but it wraps up the object and returns its starting
address.

chunk_size, base, next_free, alignment_mask, size, room

returns the appropriate class variables.

grow_fast

places a character on the obstack without checking if there is enough room.

blank_fast

like blank, but without checking if there is enough room.

shrink(int n)

shrink the current chunk by n bytes.

contains(void* addr)

returns true if the Obstack holds the address addr.

Here is a lightly edited version of the original C documentation:

These functions operate a stack of objects. Each object starts life
small, and may grow to maturity. (Consider building a word syllable
by syllable.) An object can move while it is growing. Once it has
been "finished" it never changes address again. So the "top of the
stack" is typically an immature growing object, while the rest of the
stack is of mature, fixed size and fixed address objects.

These routines grab large chunks of memory, using the GNU C++ new
operator. On occasion, they free chunks, via delete.

Each independent stack is represented by a Obstack.

One motivation for this package is the problem of growing char strings
in symbol tables. Unless you are a "fascist pig with a read-only mind"
[Gosper's immortal quote from HAKMEM item 154, out of context] you
would not like to put any arbitrary upper limit on the length of your
symbols.

In practice this often means you will build many short symbols and a
few long symbols. At the time you are reading a symbol you don't know
how long it is. One traditional method is to read a symbol into a
buffer, realloc()ating the buffer every time you try to read a
symbol that is longer than the buffer. This is beaut, but you still will
want to copy the symbol from the buffer to a more permanent
symbol-table entry say about half the time.

With obstacks, you can work differently. Use one obstack for all symbol
names. As you read a symbol, grow the name in the obstack gradually.
When the name is complete, finalize it. Then, if the symbol exists already,
free the newly read name.

The way we do this is to take a large chunk, allocating memory from
low addresses. When you want to build a symbol in the chunk you just
add chars above the current "high water mark" in the chunk. When you
have finished adding chars, because you got to the end of the symbol,
you know how long the chars are, and you can create a new object.
Mostly the chars will not burst over the highest address of the chunk,
because you would typically expect a chunk to be (say) 100 times as
long as an average object.

In case that isn't clear, when we have enough chars to make up
the object, they are already contiguous in the chunk (guaranteed)
so we just point to it where it lies. No moving of chars is
needed and this is the second win: potentially long strings need
never be explicitly shuffled. Once an object is formed, it does not
change its address during its lifetime.

When the chars burst over a chunk boundary, we allocate a larger
chunk, and then copy the partly formed object from the end of the old
chunk to the beginning of the new larger chunk. We then carry on
accreting characters to the end of the object as we normally would.

A special version of grow is provided to add a single char at a time
to a growing object.

Summary:

We allocate large chunks.

We carve out one object at a time from the current chunk.

Once carved, an object never moves.

We are free to append data of any size to the currently growing object.

Exactly one object is growing in an obstack at any one time.

You can run one obstack per control block.

You may have as many control blocks as you dare.

Because of the way we do it, you can `unwind' a obstack back to a
previous state. (You may remove objects much as you would with a stack.)

The obstack data structure is used in many places in the GNU C++ compiler.

Differences from the the GNU C version

The obvious differences stemming from the use of classes and
inline functions instead of structs and macros. The C
init and begin macros are replaced by constructors.

Overloaded function names are used for grow (and others),
rather than the C grow, grow0, etc.

All dynamic allocation uses the the built-in new operator.
This restricts flexibility by a little, but maintains compatibility
with usual C++ conventions.

There are now two versions of finish:

finish() behaves like the C version.

finish(char terminator) adds terminator, and then calls
finish(). This enables the normal invocation of finish(0) to
wrap up a string being grown character-by-character.

There are special versions of grow(const char* s) and
copy(const char* s) that add the null-terminated string s
after computing its length.

An AllocRing is a bounded ring (circular list), each of whose elements
contains a pointer to some space allocated via new
char[some_size]. The entries are used cyclicly. The size, n, of the
ring is fixed at construction. After that, every nth use of the ring
will reuse (or reallocate) the same space. AllocRings are needed in
order to temporarily hold chunks of space that are needed transiently,
but across constructor-destructor scopes. They mainly useful for storing
strings containing formatted characters to print across various
functions and coercions. These strings are needed across routines, so
may not be deleted in any one of them, but should be recovered at some
point. In other words, an AllocRing is an extremely simple minded
garbage collection mechanism. The GNU C++ library used to use one
AllocRing for such formatting purposes, but it is being phased out,
and is now only used by obsolete functions.
These days, AllocRings are probably not very useful.

Support includes:

AllocRing a(int n)

constructs an Alloc ring with n entries, all null.

void* mem = a.alloc(sz)

moves the ring pointer to the next entry, and reuses the space
if their is enough, also allocates space via new char[sz].

int present = a.contains(void* ptr)

returns true if ptr is held in one of the ring entries.

a.clear()

deletes all space pointed to in any entry. This is called
automatically upon destruction.

a.free(void* ptr)

If ptr is one of the entries, calls delete of the pointer,
and resets to entry pointer to null.

The String class is designed to extend GNU C++ to support
string processing capabilities similar to those in languages like
Awk. The class provides facilities that ought to be convenient
and efficient enough to be useful replacements for char*
based processing via the C string library (i.e., strcpy,
strcmp, etc.) in many applications. Many details about String
representations are described in the Representation section.

A separate SubString class supports substring extraction
and modification operations. This is implemented in a way that
user programs never directly construct or represent substrings,
which are only used indirectly via String operations.

Another separate class, Regex is also used indirectly via String
operations in support of regular expression searching, matching, and the
like. The Regex class is based entirely on the GNU Emacs regex
functions. See section 'Syntax of Regular Expressions' in GNU Emacs Manual, for a full
explanation of regular expression syntax. (For implementation details,
see the internal documentation in files `regex.h' and
`regex.c'.)

Set x, y, and z to the nil string. Note that either 0 or "" may
always be used to refer to the nil string.

String x = "Hello"; String y("Hello");

Set x and y to a copy of the string "Hello".

String x = 'A'; String y('A');

Set x and y to the string value "A"

String u = x; String v(x);

Set u and v to the same string as String x

String u = x.at(1,4); String v(x.at(1,4));

Set u and v to the length 4 substring of x starting at position 1
(counting indexes from 0).

String x("abc", 2);

Sets x to "ab", i.e., the first 2 characters of "abc".

String x = dec(20);

Sets x to "20". As here, Strings may be initialized or assigned
the results of any char* function.

There are no directly accessible forms for declaring SubString
variables.

The declaration Regex r("[a-zA-Z_][a-zA-Z0-9_]*"); creates
a compiled regular expression suitable for use in String
operations described below. (In this case, one that matches any
C++ identifier). The first argument may also be a String.
Be careful in distinguishing the role of backslashes in quoted
GNU C++ char* constants versus those in Regexes. For example, a Regex
that matches either one or more tabs or all strings beginning
with "ba" and ending with any number of occurrences of "na"
could be declared as Regex r = "\\(\t+\\)\\|\\(ba\\(na\\)*\\)"
Note that only one backslash is needed to signify the tab, but
two are needed for the parenthesization and virgule, since the
GNU C++ lexical analyzer decodes and strips backslashes before
they are seen by Regex.

There are three additional optional arguments to the Regex constructor
that are less commonly useful:

fast (default 0)

fast may be set to true (1) if the Regex should be
"fast-compiled". This causes an additional compilation step that
is generally worthwhile if the Regex will be used many times.

bufsize (default max(40, length of the string))

This is an estimate of the size of the internal compiled
expression. Set it to a larger value if you know that the
expression will require a lot of space. If you do not know,
do not worry: realloc is used if necessary.

transtable (default none == 0)

The address of a byte translation table (a char[256]) that
translates each character before matching.

As a convenience, several Regexes are predefined and usable in
any program. Here are their declarations from `String.h'.

The usual lexicographic relational operators (==, !=, <, <=, >, >=)
are defined. A functional form compare(String, String) is also
provided, as is fcompare(String, String), which compares
Strings without regard for upper vs. lower case.

All other matching and searching operations are based on some form of the
(non-public) match and search functions. match and
search differ in that match attempts to match only at the
given starting position, while search starts at the position, and
then proceeds left or right looking for a match. As seen in the following
examples, the second optional startpos argument to functions using
match and search specifies the starting position of the
search: If non-negative, it results in a left-to-right search starting at
position startpos, and if negative, a right-to-left search starting
at position x.length() + startpos. In all cases, the index returned
is that of the beginning of the match, or -1 if there is no match.

Three String functions serve as front ends to search and match.
index performs a search, returning the index, matches performs
a match, returning nonzero (actually, the length of the match) on success,
and contains is a boolean function performing either a search or
match, depending on whether an index argument is provided:

x.index("lo")

returns the zero-based index of the leftmost occurrence of
substring "lo" (3, in this case). The argument may be a
String, SubString, char, char*, or Regex.

x.index("l", 2)

returns the index of the first of the leftmost occurrence of "l"
found starting the search at position x[2], or 2 in this case.

x.index("l", -1)

returns the index of the rightmost occurrence of "l", or 3 here.

x.index("l", -3)

returns the index of the rightmost occurrence of "l" found by
starting the search at the 3rd to the last position of x,
returning 2 in this case.

pos = r.search("leo", 3, len, 0)

returns the index of r in the char* string of length 3,
starting at position 0, also placing the length of the match
in reference parameter len.

x.contains("He")

returns nonzero if the String x contains the substring "He". The
argument may be a String, SubString, char, char*, or Regex.

x.contains("el", 1)

returns nonzero if x contains the substring "el" at position 1.
As in this example, the second argument to contains,
if present, means to match the substring only at that position,
and not to search elsewhere in the string.

x.contains(RXwhite);

returns nonzero if x contains any whitespace (space, tab, or
newline). Recall that RXwhite is a global whitespace Regex.

x.matches("lo", 3)

returns nonzero if x starting at position 3 exactly matches "lo", with
no trailing characters (as it does in this example).

x.matches(r)

returns nonzero if String x as a whole matches Regex r.

int f = x.freq("l")

returns the number of distinct, nonoverlapping matches to the argument
(2 in this case).

Substrings may be extracted via the at, before,
through, from, and after functions.
These behave as either lvalues or rvalues.

z = x.at(2, 3)

sets String z to be equal to the length 3 substring of String x
starting at zero-based position 2, setting z to "llo" in this
case. A nil String is returned if the arguments don't make sense.

x.at(2, 2) = "r"

Sets what was in positions 2 to 3 of x to "r", setting x to
"Hero" in this case. As indicated here, SubString assignments may
be of different lengths.

x.at("He") = "je";

x("He") is the substring of x that matches the first occurrence of
it's argument. The substitution sets x to "jello". If "He" did
not occur, the substring would be nil, and the assignment would
have no effect.

x.at("l", -1) = "i";

replaces the rightmost occurrence of "l" with "i", setting x to
"Helio".

z = x.at(r)

sets String z to the first match in x of Regex r, or "ello" in this
case. A nil String is returned if there is no match.

z = x.before("o")

sets z to the part of x to the left of the first occurrence of
"o", or "Hell" in this case. The argument may also be a String,
SubString, or Regex. (If there is no match, z is set to "".)

x.before("ll") = "Bri";

sets the part of x to the left of "ll" to "Bri", setting x to
"Brillo".

z = x.before(2)

sets z to the part of x to the left of x[2], or "He" in this
case.

z = x.after("Hel")

sets z to the part of x to the right of "Hel", or "lo" in this
case.

z = x.through("el")

sets z to the part of x up and including "el", or "Hel" in this case.

z = x.from("el")

sets z to the part of x from "el" to the end, or "ello" in this case.

x.after("Hel") = "p";

sets x to "Help";

z = x.after(3)

sets z to the part of x to the right of x[3] or "o" in this case.

z = " ab c"; z = z.after(RXwhite)

sets z to the part of its old string to the right of the first
group of whitespace, setting z to "ab c"; Use gsub(below) to
strip out multiple occurrences of whitespace or any pattern.

x[0] = 'J';

sets the first element of x to 'J'. x[i] returns a reference to
the ith element of x, or triggers an error if i is out of range.

common_prefix(x, "Help")

returns the String containing the common prefix of the two Strings
or "Hel" in this case.

common_suffix(x, "to")

returns the String containing the common suffix of the two Strings
or "o" in this case.

sets up to 10 elements of String array words to the parts of z
separated by whitespace, and returns the number of parts actually
encountered (5 in this case). Here, words[0] = "this", words[1] =
"string", etc. The last argument may be any of the usual.
If there is no match, all of z ends up in words[0]. The words array
is not dynamically created by split.

int nmatches x.gsub("l","ll")

substitutes all original occurrences of "l" with "ll", setting x
to "Hellllo". The first argument may be any of the usual,
including Regex. If the second argument is "" or 0, all
occurrences are deleted. gsub returns the number of matches
that were replaced.

z = x + y; z.del("loworl");

deletes the leftmost occurrence of "loworl" in z, setting z to
"Held".

z = reverse(x)

sets z to the reverse of x, or "olleH".

z = upcase(x)

sets z to x, with all letters set to uppercase, setting z to "HELLO"

z = downcase(x)

sets z to x, with all letters set to lowercase, setting z to "hello"

z = capitalize(x)

sets z to x, with the first letter of each word set to uppercase,
and all others to lowercase, setting z to "Hello"

can be used to extract the char* char array. This
coercion is useful for sending a String as an argument to any
function expecting a const char* argument (like
atoi, and File::open). This operator must be
used with care, since the conversion returns a pointer
to String internals without copying the characters:
The resulting (char*) is only valid until
the next String operation, and you must not modify it.
(The conversion is defined to return a const
value so that GNU C++ will produce warning and/or error
messages if changes are attempted.)

Integers may be up to b * ((1 << b) - 1) bits long, where
b is the number of bits per short (typically 1048560 bits when
b = 16). The implementation assumes that a long is at least
twice as long as a short. This assumption hides beneath almost all
primitive operations, and would be very difficult to change. It also relies
on correct behavior of unsigned arithmetic operations.

Some of the arithmetic algorithms are very loosely based on those
provided in the MIT Scheme `bignum.c' release, which is
Copyright (c) 1987 Massachusetts Institute of Technology. Their use
here falls within the provisions described in the Scheme release.

Integers may be constructed in the following ways:

Integer x;

Declares an uninitialized Integer.

Integer x = 2; Integer y(2);

Set x and y to the Integer value 2;

Integer u(x); Integer v = x;

Set u and v to the same value as x.

Method: long Integer::as_long()const

Used to coerce an Integer back into longs via the long
coercion operator. If the Integer cannot fit into a long, this returns
MINLONG or MAXLONG (depending on the sign) where MINLONG is the most
negative, and MAXLONG is the most positive representable long.

Method: int Integer::fits_in_long()const

Returns true iff the Integer is < MAXLONG and > MINLONG.

Method: double Integer::as_double()const

Coerce the Integer to a double, with potential
loss of precision.
+/-HUGE is returned if the Integer cannot fit into a double.

Method: int Integer::fits_in_double()const

Returns true iff the Integer can fit into a double.

All of the usual arithmetic operators are provided (+, -, *, /,
%, +=, ++, -=, --, *=, /=, %=, ==, !=, <, <=, >, >=). All operators
support special versions for mixed arguments of Integers and regular
C++ longs in order to avoid useless coercions, as well as to allow
automatic promotion of shorts and ints to longs, so that they may be
applied without additional Integer coercion operators. The only
operators that behave differently than the corresponding int or long
operators are ++ and --. Because C++ does not
distinguish prefix from postfix application, these are declared as
void operators, so that no confusion can result from applying
them as postfix. Thus, for Integers x and y, ++x; y = x; is
correct, but y = ++x; and y = x++; are not.

Bitwise operators (~, &, |, ^, <<,
>>, &=, |=, ^=, <<=, >>=) are
also provided. However, these operate on sign-magnitude, rather than
two's complement representations. The sign of the result is arbitrarily
taken as the sign of the first argument. For example, Integer(-3)
& Integer(5) returns Integer(-1), not -3, as it would using
two's complement. Also, ~, the complement operator, complements
only those bits needed for the representation. Bit operators are also
provided in the BitSet and BitString classes. One of these classes
should be used instead of Integers when the results of bit manipulations
are not interpreted numerically.

The following utility functions are also provided. (All arguments
are Integers unless otherwise noted).

Sets x to a Rational value close to 1.2. Any double precision value
may be used to construct a Rational. The Rational will possess
exactly as much precision as the double. Double values that do
not have precise floating point equivalents (like 1.2) produce
similarly imprecise rational values.

Rational x(Integer(123), Integer(4567));

Sets x to the Rational value 123/4567.

Rational u(x); Rational v = x;

Set u and v to the same value as x.

double(Rational x)

A Rational may be coerced to a double with potential
loss of precision. +/-HUGE is returned if it will not fit.

Rational abs(x)

returns the absolute value of x.

void x.negate()

negates x.

void x.invert()

sets x to 1/x.

int sign(x)

returns 0 if x is zero, 1 if positive, and -1 if negative.

Rational sqr(x)

returns x * x.

Rational pow(x, Integer y)

returns x to the y power.

Integer x.numerator()

returns the numerator.

Integer x.denominator()

returns the denominator.

Integer floor(x)

returns the greatest Integer less than x.

Integer ceil(x)

returns the least Integer greater than x.

Integer trunc(x)

returns the Integer part of x.

Integer round(x)

returns the nearest Integer to x.

int compare(x, y)

returns a negative, zero, or positive number signifying whether x is
less than, equal to, or greater than y.

ostream << x;

prints x in the form num/den, or just num if the denominator is one.

istream >> x;

reads x in the form num/den, or just num in which case the
denominator is set to one.

Class Complex is implemented in a way similar to that
described by Stroustrup. In keeping with libg++ conventions,
the class is named Complex, not complex.
Complex arithmetic and relational operators are provided
(+, -, *, /, +=, -=, *=, /=, ==, !=).
Attempted division by (0, 0) triggers an exception.

Complex numbers may be constructed and used in the following ways:

Complex x;

Declares an uninitialized Complex.

Complex x = 2; Complex y(2.0);

Set x and y to the Complex value (2.0, 0.0);

Complex x(2, 3);

Sets x to the Complex value (2, 3);

Complex u(x); Complex v = x;

Set u and v to the same value as x.

double real(Complex& x);

returns the real part of x.

double imag(Complex& x);

returns the imaginary part of x.

double abs(Complex& x);

returns the magnitude of x.

double norm(Complex& x);

returns the square of the magnitude of x.

double arg(Complex& x);

returns the argument (amplitude) of x.

Complex polar(double r, double t = 0.0);

returns a Complex with abs of r and arg of t.

Complex conj(Complex& x);

returns the complex conjugate of x.

Complex cos(Complex& x);

returns the complex cosine of x.

Complex sin(Complex& x);

returns the complex sine of x.

Complex cosh(Complex& x);

returns the complex hyperbolic cosine of x.

Complex sinh(Complex& x);

returns the complex hyperbolic sine of x.

Complex exp(Complex& x);

returns the exponential of x.

Complex log(Complex& x);

returns the natural log of x.

Complex pow(Complex& x, long p);

returns x raised to the p power.

Complex pow(Complex& x, Complex& p);

returns x raised to the p power.

Complex sqrt(Complex& x);

returns the square root of x.

ostream << x;

prints x in the form (re, im).

istream >> x;

reads x in the form (re, im), or just (re) or re in which case the
imaginary part is set to zero.

Classes Fix16, Fix24, Fix32, and Fix48
support operations on 16, 24, 32, or 48 bit quantities that are
considered as real numbers in the range [-1, +1). Such numbers are
often encountered in digital signal processing applications. The classes
may be be used in isolation or together. Class Fix32
operations are entirely self-contained. Class Fix16 operations
are self-contained except that the multiplication operation Fix16
* Fix16 returns a Fix32. Fix24 and Fix48 are
similarly related.

The standard arithmetic and relational operations are supported
(=, +, -, *, /, <<, >>,
+=, -=, *=, /=, <<=, >>=,
==, !=, <, <=, >, >=).
All operations include provisions for special handling in cases where
the result exceeds +/- 1.0. There are two cases that may be handled
separately: "overflow" where the results of addition and subtraction
operations go out of range, and all other "range errors" in which
resulting values go off-scale (as with division operations, and
assignment or initialization with off-scale values). In signal
processing applications, it is often useful to handle these two cases
differently. Handlers take one argument, a reference to the integer
mantissa of the offending value, which may then be manipulated. In
cases of overflow, this value is the result of the (integer) arithmetic
computation on the mantissa; in others it is a fully saturated (i.e.,
most positive or most negative) value. Handling may be reset to any of
several provided functions or any other user-defined function via
set_overflow_handler and set_range_error_handler. The
provided functions for Fix16 are as follows (corresponding
functions are also supported for the others).

Fix16_overflow_saturate

The default overflow handler. Results are "saturated": positive results
are set to the largest representable value (binary 0.111111...), and
negative values to -1.0.

Fix16_ignore

Performs no action. For overflow, this will allow addition and
subtraction operations to "wrap around" in the same manner
as integer arithmetic, and for saturation, will leave values saturated.

Fix16_overflow_warning_saturate

Prints a warning message on standard error, then saturates the results.

Constructs fixed precision objects from double precision values.
Attempting to initialize to a value outside the range invokes
the range_error handler, except, as a convenience,
initialization to 1.0 sets the variable to the most positive
representable value (binary 0.1111111...) without invoking the handler.

short& mantissa(a); long& mantissa(b);

return a * pow(2, 15) or b * pow(2, 31) as an integer. These
are returned by reference, to enable "manual" data manipulation.

libg++ provides several different classes supporting the use
and manipulation of collections of bits in different ways.

Class Integer provides "integer" semantics. It supports
manipulation of bits in ways that are often useful when treating bit arrays
as numerical (integer) quantities. This class is described elsewhere.

BitSets are logically infinite. Their space is dynamically altered to
adjust to the smallest number of consecutive bits actually required to
represent the sets. Integers also have this property. BitStrings are
logically finite, but their sizes are internally dynamically managed to
maintain proper length. This means that, for example, BitStrings are
concatenatable while BitSets and Integers are not.

BitSet32 and BitSet256 have precisely the same properties as BitSets,
except that they use constant fixed length bit vectors.

While all classes support basic unary and binary operations ~, &,
|, ^, -, the semantics differ. BitSets perform bit operations that
precisely mirror those for infinite sets. For example, complementing an
empty BitSet returns one representing an infinite number of set bits.
Operations on BitStrings and Integers operate only on those bits
actually present in the representation. For BitStrings and Integers,
the the & operation returns a BitString with a length equal to
the minimum length of the operands, and |, ^ return one with
length of the maximum.

Only BitStrings support substring extraction and bit pattern matching.

BitSets are objects that contain logically infinite sets of nonnegative
integers. Representational details are discussed in the Representation
chapter. Because they are logically infinite, all BitSets possess a
trailing, infinitely replicated 0 or 1 bit, called the "virtual bit", and
indicated via 0* or 1*.

BitSet32 and BitSet256 have they same properties, except they are
of fixed length, and thus have no virtual bit.

BitSets may be constructed as follows:

BitSet a;

declares an empty BitSet.

BitSet a = atoBitSet("001000");

sets a to the BitSet 0010*, reading left-to-right. The "0*"
indicates that the set ends with an infinite number of zero
(clear) bits.

BitSet a = atoBitSet("00101*");

sets a to the BitSet 00101*, where "1*" means that the set ends
with an infinite number of one (set) bits.

BitSet a = longtoBitSet((long)23);

sets a to the BitSet 111010*, the binary representation of decimal 23.

BitSet a = utoBitSet((unsigned)23);

sets a to the BitSet 111010*, the binary representation of decimal 23.

The following functions and operators are provided (Assume the
declaration of BitSets a = 0011010*, b = 101101*, throughout, as
examples).

~a

returns the complement of a, or 1100101* in this case.

a.complement()

sets a to ~a.

a & b; a &= b;

returns a intersected with b, or 0011010*.

a | b; a |= b;

returns a unioned with b, or 1011111*.

a - b; a -= b;

returns the set difference of a and b, or 000010*.

a ^ b; a ^= b;

returns the symmetric difference of a and b, or 1000101*.

a.empty()

returns true if a is an empty set.

a == b;

returns true if a and b contain the same set.

a <= b;

returns true if a is a subset of b.

a < b;

returns true if a is a proper subset of b;

a != b; a >= b; a > b;

are the converses of the above.

a.set(7)

sets the 7th (counting from 0) bit of a, setting a to 001111010*

a.clear(2)

clears the 2nd bit bit of a, setting a to 00011110*

a.clear()

clears all bits of a;

a.set()

sets all bits of a;

a.invert(0)

complements the 0th bit of a, setting a to 10011110*

a.set(0,1)

sets the 0th through 1st bits of a, setting a to 110111110*
The two-argument versions of clear and invert are similar.

a.test(3)

returns true if the 3rd bit of a is set.

a.test(3, 5)

returns true if any of bits 3 through 5 are set.

int i = a[3]; a[3] = 0;

The subscript operator allows bits to be inspected and changed
via standard subscript semantics, using a friend class BitSetBit.
The use of the subscript operator a[i] rather than a.test(i)
requires somewhat greater overhead.

a.first(1) or a.first()

returns the index of the first set bit of a (2 in this case),
or -1 if no bits are set.

a.first(0)

returns the index of the first clear bit of a (0 in this case),
or -1 if no bits are clear.

a.next(2, 1) or a.next(2)

returns the index of the next bit after position 2 that is set (3
in this case) or -1. first and next may be used as
iterators, as in
for (int i = a.first(); i >= 0; i = a.next(i))....

a.last(1)

returns the index of the rightmost set bit, or -1 if there or no set
bits or all set bits.

a.prev(3, 0)

returns the index of the previous clear bit before position 3.

a.count(1)

returns the number of set bits in a, or -1 if there are
an infinite number.

BitStrings are objects that contain arbitrary-length strings of
zeroes and ones. BitStrings possess some features that make them
behave like sets, and others that behave as strings. They are
useful in applications (such as signature-based algorithms) where
both capabilities are needed. Representational details are
discussed in the Representation chapter. Most capabilities are
exact analogs of those supported in the BitSet and String
classes. A BitSubString is used with substring operations along
the same lines as the String SubString class. A BitPattern class
is used for masked bit pattern searching.

Only a default constructor is supported. The declaration
BitString a; initializes a to be an empty BitString.
BitStrings may often be initialized via atoBitString
and longtoBitString.

Set operations ( ~, complement, &, &=, |, |=, -, ^, ^=)
behave just as the BitSet versions, except that there is no
"virtual bit": complementing complements only those bits in the
BitString, and all binary operations across unequal length
BitStrings assume a virtual bit of zero. The & operation
returns a BitString with a length equal to the minimum length of
the operands, and |, ^ return one with length of the
maximum.

Set-based relational operations (==, !=, <=, <, >=, >)
follow the same rules. A string-like lexicographic comparison
function, lcompare, tests the lexicographic relation between
two BitStrings. For example, lcompare(1100, 0101) returns 1,
since the first BitString starts with 1 and the second with 0.

Individual bit setting, testing, and iterator operations
(set, clear, invert, test, first, next, last, prev)
are also like those for BitSets. BitStrings are automatically
expanded when setting bits at positions greater than their
current length.

The string-based capabilities are just as those for class String.
BitStrings may be concatenated (+, +=), searched
(index, contains, matches), and extracted into
BitSubStrings (before, at, after) which may be assigned and
otherwise manipulated. Other string-based utility functions
(reverse, common_prefix, common_suffix) are also provided.
These have the same capabilities and descriptions as those
for Strings.

String-oriented operations can also be performed with a mask via
class BitPattern. BitPatterns consist of two BitStrings, a
pattern and a mask. On searching and matching, bits in the pattern
that correspond to 0 bits in the mask are ignored. (The mask may
be shorter than the pattern, in which case trailing mask bits are
assumed to be 0). The pattern and mask are both public variables,
and may be individually subjected to other bit operations.

Converting to char* and printing ((atoBitString,
atoBitPattern, printon, ostream <<)) are also as in BitSets,
except that no virtual bit is used, and an 'X' in a BitPattern means
that the pattern bit is masked out.

return a with 2 zeros prepended, setting a to 0001010110. (Note
the necessary confusion of << and >> operators. For consistency
with the integer versions, << shifts low bits to high, even though
they are printed low bits first.)

The two classes RNG and Random are used together to
generate a variety of random number distributions. A distinction must
be made between random number generators, implemented by class
RNG, and random number distributions. A random number
generator produces a series of randomly ordered bits. These bits can be
used directly, or cast to other representations, such as a floating
point value. A random number generator should produce a uniform
distribution. A random number distribution, on the other hand, uses the
randomly generated bits of a generator to produce numbers from a
distribution with specific properties. Each instance of Random
uses an instance of class RNG to provide the raw, uniform
distribution used to produce the specific distribution. Several
instances of Random classes can share the same instance of
RNG, or each instance can use its own copy.

Random distributions are constructed from members of class RNG,
the actual random number generators. The RNG class contains no
data; it only serves to define the interface to random number
generators. The RNG::asLong member returns an unsigned long
(typically 32 bits) of random bits. Applications that require a number
of random bits can use this directly. More often, these random bits are
transformed to a uniform random number:

using either asFloat or asDouble. It is intended that
asFloat and asDouble return differing precisions;
typically, asDouble will draw two random longwords and transform
them into a legal double, while asFloat will draw a single
longword and transform it into a legal float. These members are
used by subclasses of the Random class to implement a variety of
random number distributions.

Class ACG is a variant of a Linear Congruential Generator
(Algorithm M) described in Knuth, Art of Computer Programming, Vol
III. This result is permuted with a Fibonacci Additive Congruential
Generator to get good independence between samples. This is a very high
quality random number generator, although it requires a fair amount of
memory for each instance of the generator.

The ACG::ACG constructor takes two parameters: the seed and the
size. The seed is any number to be used as an initial seed. The
performance of the generator depends on having a distribution of bits
through the seed. If you choose a number in the range of 0 to 31, a
seed with more bits is chosen. Other values are deterministically
modified to give a better distribution of bits. This provides a good
random number generator while still allowing a sequence to be repeated
given the same initial seed.

The size parameter determines the size of two tables used in the
generator. The first table is used in the Additive Generator; see the
algorithm in Knuth for more information. In general, this table is
size longwords long. The default value, used in the algorithm in
Knuth, gives a table of 220 bytes. The table size affects the period of
the generators; smaller values give shorter periods and larger tables
give longer periods. The smallest table size is 7 longwords, and the
longest is 98 longwords. The size parameter also determines the
size of the table used for the Linear Congruential Generator. This value
is chosen implicitly based on the size of the Additive Congruential
Generator table. It is two powers of two larger than the power of two
that is larger than size. For example, if size is 7, the
ACG table is 7 longwords and the LCG table is 128 longwords. Thus, the
default size (55) requires 55 + 256 longwords, or 1244 bytes. The
largest table requires 2440 bytes and the smallest table requires 100
bytes. Applications that require a large number of generators or
applications that aren't so fussy about the quality of the generator may
elect to use the MLCG generator.

The MLCG class implements a Multiplicative Linear
Congruential Generator. In particular, it is an implementation of the
double MLCG described in "Efficient and Portable Combined Random
Number Generators" by Pierre L'Ecuyer, appearing in
Communications of the ACM, Vol. 31. No. 6. This generator has a
fairly long period, and has been statistically analyzed to show that it
gives good inter-sample independence.

The MLCG::MLCG constructor has two parameters, both of which are
seeds for the generator. As in the MLCG generator, both seeds are
modified to give a "better" distribution of seed digits. Thus, you can
safely use values such as `0' or `1' for the seeds. The MLCG
generator used much less state than the ACG generator; only two
longwords (8 bytes) are needed for each generator.

A random number generator may be declared by first declaring a
RNG and then a Random. For example, ACG gen(10, 20);
NegativeExpntl rnd (1.0, &gen); declares an additive congruential
generator with seed 10 and table size 20, that is used to generate
exponentially distributed values with mean of 1.0.

The virtual member Random::operator() is the common way of
extracting a random number from a particular distribution. The base
class, Random does not implement operator(). This is
performed by each of the subclasses. Thus, given the above declaration
of rnd, new random values may be obtained via, for example,
double next_exp_rand = rnd(); Currently, the following subclasses
are provided.

The binomial distribution models successfully drawing items from
a pool. The first parameter to the constructor, n, is the
number of items in the pool, and the second parameter, u,
is the probability of each item being successfully drawn. The
member asDouble returns the number of samples drawn from
the pool. Although it is not checked, it is assumed that
n>0 and 0 <= u <= 1. The remaining members allow
you to read and set the parameters.

The Geometric class implements a discrete geometric
distribution. The first parameter to the constructor,
mean, is the mean of the distribution. Although it is not
checked, it is assumed that 0 <= mean <= 1.
Geometric() returns the number of uniform random samples
that were drawn before the sample was larger than mean.
This quantity is always greater than zero.

The HyperGeometric class implements the hypergeometric
distribution. The first parameter to the constructor,
mean, is the mean and the second, variance, is the
variance. The remaining members allow you to inspect and change
the mean and variance.

The Normalclass implements the normal distribution. The
first parameter to the constructor, mean, is the mean and
the second, variance, is the variance. The remaining
members allow you to inspect and change the mean and variance.
The LogNormal class is a subclass of Normal.

The LogNormalclass implements the logarithmic normal
distribution. The first parameter to the constructor,
mean, is the mean and the second, variance, is the
variance. The remaining members allow you to inspect and change
the mean and variance. The LogNormal class is a subclass
of Normal.

The DiscreteUniform class implements a uniform random variable over
the closed interval ranging from [low..high]. The first parameter
to the constructor is low, and the second is high, although
the order of these may be reversed. The remaining members allow you to
inspect and change low and high.

The Uniform class implements a uniform random variable over the
open interval ranging from [low..high). The first parameter to
the constructor is low, and the second is high, although
the order of these may be reversed. The remaining members allow you to
inspect and change low and high.

The Weibull class implements a weibull distribution with
parameters alpha and beta. The first parameter to
the class constructor is alpha, and the second parameter
is beta. The remaining members allow you to inspect and
change alpha and beta.

The RandomInteger class is not a subclass of Random,
but a stand-alone integer-oriented class that is dependent on the
RNG classes. RandomInteger returns random integers uniformly from
the closed interval [low..high]. The first parameter to the
constructor is low, and the second is high, although
both are optional. The last argument is always a generator.
Additional members allow you to inspect and change low and
high. Random integers are generated using asInt() or
asLong(). Operator syntax (()) is also available as a
shorthand for asLong(). Because RandomInteger is often
used in simulations for which uniform random integers are desired over
a variety of ranges, asLong() and asInt have high
as an optional argument. Using this optional argument produces a
single value from the new range, but does not change the default
range.

Class SampleHistogram is a derived class of
SampleStatistic that supports collection and display of samples
in bucketed intervals. It supports the following in addition to
SampleStatisic operations.

SampleHistogram h(double lo, double hi, double width);

declares and initializes h to have buckets of size width from lo to hi.
If the optional argument width is not specified, 10 buckets are
created. The first bucket and also holds samples less than lo,
and the last one holds samples greater than hi.

The CursesWindow class is a repackaging of standard
curses library features into a class. It relies on `curses.h'.

The supplied `curses.h' is a fairly conservative declaration
of curses library features, and does not include features like
"screen" or X-window support. It is, for the most part, an
adaptation, rather than an improvement of C-based `curses.h'
files. The only substantive changes are the declarations of
many functions as inline functions rather than macros, which
was done solely to allow overloading.

The CursesWindow class encapsulates curses window functions
within a class. Only those functions that control windows are included:
Terminal control functions and macros like cbreak are not part
of the class. All CursesWindows member functions have names
identical to the corresponding curses library functions, except that the
"w" prefix is generally dropped. Descriptions of these functions may
be found in your local curses library documentation.

A CursesWindow may be declared via

CursesWindow w(WINDOW* win)

attaches w to the existing WINDOW* win. This is constructor is normally
used only in the following special case.

CursesWindow w(stdscr)

attaches w to the default curses library standard screen window.

CursesWindow w(int lines, int cols, int begin_y, int begin_x)

attaches to an allocated curses window with the indicated size and
screen position.

attaches to a subwindow of w created via the curses `subwin' command.
If ar is sent as `r', the origin (by, bx) is relative to the parent
window, else it is absolute.

The class maintains a static counter that is used in order to
automatically call the curses library initscr and endscr
functions at the proper times. These need not, and should not be
called "manually".

CursesWindows maintain a tree of their subwindows. Upon
destruction of a CursesWindow, all of their subwindows are
also invalidated if they had not previously been destroyed.

It is possible to traverse trees of subwindows via the following
member functions

CursesWindow* w.parent()

returns a pointer to the parent of the subwindow, or 0 if there is none.

CursesWindow* w.child()

returns the first child subwindow of the window, or 0 if there is none.

CursesWindow* w.sibling()

returns the next sibling of the subwindow, or 0 if there is none.

For example, to call some function visit for all subwindows
of a window, you could write

The files `g++-include/List.hP' and `g++-include/List.ccP'
provide pseudo-generic Lisp-type List classes. These lists are homogeneous
lists, more similar to lists in statically typed functional languages like
ML than Lisp, but support operations very similar to those found in Lisp.
Any particular kind of list class may be generated via the genclass
shell command. However, the implementation assumes that the base class
supports an equality operator ==. All equality tests use the
== operator, and are thus equivalent to the use of equal, not
eq in Lisp.

All list nodes are created dynamically, and managed via reference counts.
List variables are actually pointers to these list nodes.
Lists may also be traversed via Pixes, as described in the section
describing Pixes. See section Pseudo-indexes

Supported operations are mirrored closely after those in Lisp. Generally,
operations with functional forms are constructive, functional operations,
while member forms (often with the same name) are sometimes
procedural, possibly destructive operations.

As with Lisp, destructive operations are supported. Programmers
are allowed to change head and tail fields in any fashion, creating
circular structures and the like. However, again as with Lisp, some
operations implicitly assume that they are operating on pure lists, and
may enter infinite loops when presented with improper lists. Also, the
reference-counting storage management facility may fail to reclaim
unused circularly-linked nodes.

Several Lisp-like higher order functions are supported (e.g., map).
Typedef declarations for the required functional forms are provided
int the `.h' file.

For purposes of illustration, assume the specification of class
intList. Common Lisp versions of supported operations are shown
in brackets for comparison purposes.

SLLists provide pseudo-generic singly linked lists. DLLists provide
doubly linked lists. The lists are designed for the simple maintenance
of elements in a linked structure, and do not provide the more extensive
operations (or node-sharing) of class List. They behave similarly
to the slist and similar classes described by Stroustrup.

All list nodes are created dynamically. Assignment is performed via
copying.

AVecs provide additional arithmetic operations. All vector-by-vector
operators generate an error if the vectors are not the same length. The
following operations are provided, for AVecs a, b and
base element (scalar) s.

a = b;

Copies b to a. a and b must be the same size.

a = s;

fills all elements of a with the value s. a is not resized.

a + s; a - s; a * s; a / s

adds, subtracts, multiplies, or divides each element of a with the scalar.

a += s; a -= s; a *= s; a /= s;

adds, subtracts, multiplies, or divides the scalar into a.

a + b; a - b; product(a, b), quotient(a, b)

adds, subtracts, multiplies, or divides corresponding elements of a and b.

Note that it is possible to apply vector versions other arithmetic
operators via the mapping functions. For example, to set vector b
to the cosines of doubleVec a, use b = map(cos, a);.
This is often more efficient than performing the operations
in an element-by-element fashion.

Plexes may have arbitrary upper and lower index bounds. For example
a Plex may be declared to run from indices -10 .. 10.

Plexes may be dynamically expanded at both the lower and upper bounds
of the array in steps of one element.

Only elements that have been specifically initialized or added may
be accessed.

Elements may be accessed via indices. Indices are always checked for
validity at run time. Plexes may be traversed via simple variations of
standard array indexing loops.

Plex elements may be accessed and traversed via Pixes.

Plex-to-Plex assignment and related operations on entire Plexes
are supported.

Plex classes contain methods to help programmers check the validity
of indexing and pointer operations.

Plexes form "natural" base classes for many restricted-access data
structures relying on logically contiguous indices, such as array-based
stacks and queues.

Plexes are implemented as pseudo-generic classes, and must be generated
via the genclass utility.

Four subclasses of Plexes are supported: A FPlex is a Plex that
may only grow or shrink within declared bounds; an XPlex may
dynamically grow or shrink without bounds; an RPlex is the
same as an XPlex but better supports indexing with poor
locality of reference; a MPlex may grow
or shrink, and additionally allows the logical deletion and restoration
of elements. Because these classes are virtual subclasses of the
"abstract" class Plex, it is possible to write user code
such as void f(Plex& a) ... that operates on any kind of
Plex. However, as with nearly any virtual class, specifying the
particular Plex class being used results in more efficient code.

Plexes are implemented as a linked list of IChunks. Each chunk
contains a part of the array. Chunk sizes may be specified within Plex
constructors. Default versions also exist, that use a #define'd
default. Plexes grow by filling unused space in existing chunks, if
possible, else, except for FPlexes, by adding another chunk. Whenever
Plexes grow by a new chunk, the default element constructors (i.e.,
those which take no arguments) for all chunk elements are called at
once. When Plexes shrink, destructors for the elements are not called
until an entire chunk is freed. For this reason, Plexes (like C++
arrays) should only be used for elements with default constructors and
destructors that have no side effects.

Plexes may be indexed and used like arrays, although traversal
syntax is slightly different. Even though Plexes maintain elements
in lists of chunks, they are implemented so that iteration and
other constructs that maintain locality of reference require very
little overhead over that for simple array traversal
Pix-based traversal is also supported. For example, for a plex, p,
of ints, the following traversal methods could be used.

Except for MPlexes, simply using ++i and --i works just as
well as p.next(i) and p.prev(i) when traversing by index.
Index-based traversal is generally a bit faster than Pix-based
traversal.

XPlexes and MPlexes are less than optimal for applications
in which widely scattered elements are indexed, as might occur when
using Plexes as hash tables or "manually" allocated linked lists.
In such applications, RPlexes are often preferable. RPlexes
use a secondary chunk index table that requires slightly greater,
but entirely uniform overhead per index operation.

Even though they may grow in either direction, Plexes are normally
constructed so that their "natural" growth direction is upwards,
in that default chunk construction leaves free space, if present,
at the end of the plex. However, if the chunksize arguments to
constructors are negative, they leave space at the beginning.

Declares p to be an initially zero-sized Plex with low index of zero,
and the default chunk size. For FPlexes, chunk sizes represent maximum
sizes.

Plex p(int size);

Declares p to be an initially zero-sized Plex with low index of zero,
and the indicated chunk size. If size is negative, then the Plex
is created with free space at the beginning of the Plex,
allowing more efficient add_low() operations. Otherwise, it
leaves space at the end.

Plex p(int low, int size);

Declares p to be an initially zero-sized Plex with low index of low,
and the indicated chunk size.

Plex p(int low, int high, Base initval, int size = 0);

Declares p to be a Plex with indices from low to high, initially
filled with initval, and the indicated chunk size if specified,
else the default or (high - low + 1), whichever is greater.

Plex q(p);

Declares q to be a copy of p.

p = q;

Copies Plex q into p, deleting its previous contents.

p.length()

Returns the number of elements in the Plex.

p.empty()

Returns true if Plex p contains no elements.

p.full()

Returns true if Plex p cannot be expanded. This always returns
false for XPlexes and MPlexes.

p[i]

Returns a reference to the i'th element of p. An exception (error) occurs
if i is not a valid index.

p.valid(i)

Returns true if i is a valid index into Plex p.

p.low(); p.high();

Return the minimum (maximum) valid index of the Plex, or the high (low)
fence if the plex is empty.

p.ecnef(); p.fence();

Return the index one position past the minimum (maximum) valid index.

p.next(i); i = p.prev(i);

Set i to the next (previous) index. This index may not be within bounds.

p(pix)

returns a reference to the item at Pix pix.

pix = p.first(); pix = p.last();

Return the minimum (maximum) valid Pix of the Plex, or 0
if the plex is empty.

p.next(pix); p.prev(pix);

set pix to the next (previous) Pix, or 0 if there is none.

p.owns(pix)

Returns true if the Plex contains the element associated with pix.

p.Pix_to_index(pix)

If pix is a valid Pix to an element of the Plex,
returns its corresponding index, else raises an exception.

ptr = p.index_to_Pix(i)

if i is a valid index, returns a the corresponding Pix.

p.low_element(); p.high_element();

Return a reference to the element at the minimum (maximum) valid index.
An exception occurs if the Plex is empty.

p.can_add_low(); p.can_add_high();

Returns true if the plex can be extended one element downward (upward).
These always return true for XPlex and MPlex.

j = p.add_low(x); j = p.add_high(x);

Extend the Plex by one element downward (upward). The new minimum
(maximum) index is returned.

j = p.del_low(); j = p.del_high()

Shrink the Plex by one element on the low (high) end. The new
minimum (maximum) element is returned. An exception occurs if the
Plex is empty.

p.append(q);

Append all of Plex q to the high side of p.

p.prepend(q);

Prepend all of q to the low side of p.

p.clear()

Delete all elements, resetting p to a zero-sized Plex.

p.reset_low(i);

Resets p to be indexed starting at low() = i. For example.
if p were initially declared via Plex p(0, 10, 0),
and then re-indexed via p.reset_low(5),
it could then be indexed from indices 5 .. 14.

p.fill(x)

sets all p[i] to x.

p.fill(x, lo, hi)

sets all of p[i] from lo to hi, inclusive, to x.

p.reverse()

reverses p in-place.

p.chunk_size()

returns the chunk size used for the plex.

p.error(const char * msg)

calls the resettable error handler.

MPlexes are plexes with bitmaps that allow items to be logically
deleted and restored. They behave like other plexes, but
also support the following additional and modified capabilities:

Delete the lowest (highest) undeleted element, resetting the
logical bounds of the plex to the next lowest (highest) undeleted
index. Thus, MPlex del_low() and del_high() may shrink the bounds
of the plex by more than one index.

p.adjust_bounds()

Resets the low and high bounds of the Plex to the indexes of
the lowest and highest actual undeleted elements.

int i = p.add(x)

Adds x in an unused index, if possible, else performs add_high.

p.count()

returns the number of valid (undeleted) elements.

p.available()

returns the number of available (deleted) indices.

int i = p.unused_index()

returns the index of some deleted element, if one exists,
else triggers an error. An unused element may be reused via undel.

pix = p.unused_Pix()

returns the pix of some deleted element, if one exists, else 0.
An unused element may be reused via undel.

Stacks are declared as an "abstract" class. They are currently
implemented in any of three ways.

VStack

implement fixed sized stacks via arrays.

XPStack

implement dynamically-sized stacks via XPlexes.

SLStack

implement dynamically-size stacks via linked lists.

All possess the same capabilities. They differ only in constructors.
VStack constructors require a fixed maximum capacity argument.
XPStack constructors optionally take a chunk size argument.
SLStack constructors take no argument.

Assume the declaration of a base element x.

Stack s; or Stack s(int capacity)

declares a Stack.

s.empty()

returns true if stack s is empty.

s.full()

returns true if stack s is full. XPStacks and SLStacks never become full.

s.length()

returns the current number of elements in the stack.

s.push(x)

pushes x on stack s.

x = s.pop()

pops and returns the top of stack

s.top()

returns a reference to the top of stack.

s.del_top()

pops, but does not return the top of stack. When large items are held
on the stack it is often a good idea to use top() to inspect and use
the top of stack, followed by a del_top()

Queues are declared as an "abstract" class. They are currently
implemented in any of three ways.

VQueue

implement fixed sized Queues via arrays.

XPQueue

implement dynamically-sized Queues via XPlexes.

SLQueue

implement dynamically-size Queues via linked lists.

All possess the same capabilities; they differ only in constructors.
VQueue constructors require a fixed maximum capacity argument.
XPQueue constructors optionally take a chunk size argument.
SLQueue constructors take no argument.

Assume the declaration of a base element x.

Queue q; or Queue q(int capacity);

declares a queue.

q.empty()

returns true if queue q is empty.

q.full()

returns true if queue q is full. XPQueues and SLQueues are never full.

implement PQs via Sleator and Tarjan's (JACM 1985)
splay trees. The algorithms use a version of "simple top-down
splaying" (described on page 669 of the article). The simple-splay
mechanism for priority queue functions is loosely based on the one used
by D. Jones in the C splay tree functions available from volume 14 of
the uunet.uu.net archives.

PHPQs

implement pairing heaps (as described by Fredman and
Sedgewick in Algorithmica, Vol 1, p111-129). Storage for heap elements
is managed via an internal freelist technique. The constructor allows an
initial capacity estimate for freelist space. The storage is automatically
expanded if necessary to hold new items. The deletion technique is a fast
"lazy deletion" strategy that marks items as deleted, without reclaiming
space until the items come to the top of the heap.

All PQ classes support the following operations, for some PQ class
Heap, instance h, Pix ind, and base class
variable x.

h.empty()

returns true if there are no elements in the PQ.

h.length()

returns the number of elements in h.

ind = h.enq(x)

Places x in the PQ, and returns its index.

x = h.deq()

Dequeues the minimum element of the PQ into x, or generates an error
if the PQ is empty.

h.front()

returns a reference to the minimum element.

h.del_front()

deletes the minimum element.

h.clear();

deletes all elements from h;

h.contains(x)

returns true if x is in h.

h(ind)

returns a reference to the item indexed by ind.

ind = h.first()

returns the Pix of first item in the PQ or 0 if empty.
This need not be the Pix of the least element.

These are currently implemented in several ways, differing in
representation strategy, algorithmic efficiency, and appropriateness for
various tasks. (Listed next to each are average (followed by worst-case,
if different) time complexities for [a] adding, [f] finding (via seek,
contains), [d] deleting, elements, and [c] comparing (via ==, <=) and
[m] merging (via |=, -=, &=) sets).

The different implementations differ in whether their constructors
require an argument specifying their initial capacity. Initial
capacities are required for plex and hash table based Sets. If none is
given DEFAULT_INITIAL_CAPACITY (from `<T>defs.h') is
used.

Sets support the following operations, for some class Set,
instances a and b, Pix ind, and base
element x. Since all implementations are virtual derived classes
of the <T>Set class, it is possible to mix and match operations
across different implementations, although, as usual, operations
are generally faster when the particular classes are specified
in functions operating on Sets.

Pix-based operations are more fully described in the section
on Pixes. See section Pseudo-indexes

Set a; or Set a(int initial_size);

Declares a to be an empty Set. The second version is allowed in
set classes that require initial capacity or sizing specifications.

a.empty()

returns true if a is empty.

a.length()

returns the number of elements in a.

Pix ind = a.add(x)

inserts x into a, returning its index.

a.del(x)

deletes x from a.

a.clear()

deletes all elements from a;

a.contains(x)

returns true if x is in a.

a(ind)

returns a reference to the item indexed by ind.

ind = a.first()

returns the Pix of first item in the set or 0 if the Set is empty.
For ordered Sets, this is the Pix of the least element.

These are currently implemented in several ways, differing in
representation strategy, algorithmic efficiency, and appropriateness for
various tasks. (Listed next to each are average (followed by worst-case,
if different) time complexities for [a] adding, [f] finding (via seek,
contains), [d] deleting elements).

The implementations differ in whether their constructors
require an argument to specify their initial capacity. Initial
capacities are required for plex and hash table based Bags. If none is
given DEFAULT_INITIAL_CAPACITY (from `<T>defs.h') is used.

Bags support the following operations, for some class Bag,
instances a and b, Pix ind, and base
element x. Since all implementations are virtual derived classes
of the <T>Bag class, it is possible to mix and match operations
across different implementations, although, as usual, operations
are generally faster when the particular classes are specified
in functions operating on Bags.

Pix-based operations are more fully described in the section
on Pixes. See section Pseudo-indexes

Bag a; or Bag a(int initial_size)

Declares a to be an empty Bag. The second version is allowed in
Bag classes that require initial capacity or sizing specifications.

a.empty()

returns true if a is empty.

a.length()

returns the number of elements in a.

ind = a.add(x)

inserts x into a, returning its index.

a.del(x)

deletes one occurrence of x from a.

a.remove(x)

deletes all occurrences of x from a.

a.clear()

deletes all elements from a;

a.contains(x)

returns true if x is in a.

a.nof(x)

returns the number of occurrences of x in a.

a(ind)

returns a reference to the item indexed by ind.

int = a.first()

returns the Pix of first item in the Bag or 0 if the Bag is empty.
For ordered Bags, this is the Pix of the least element.

a.next(ind)

advances ind to the Pix of next element, or 0 if there are no more.

ind = a.seek(x. Pix from = 0)

Sets ind to the Pix of the next occurrence x, or 0 if there are none.
If from is 0, the first occurrence is returned, else the following from.

Maps support associative array operations (insertion, deletion, and
membership of records based on an associated key). They require
the specification of two types, the key type and the contents type.

These are currently implemented in several ways, differing in
representation strategy, algorithmic efficiency, and appropriateness for
various tasks. (Listed next to each are average (followed by worst-case,
if different) time complexities for [a] accessing (via op [],
contains), [d] deleting elements).

Similar, but also maintain ranking information, used via
ranktoPix(int r), that returns the Pix of the
item at rank r, and rank(key) that returns the
rank of the corresponding item.
([a O(log n)], [d O(log n)]).

The different implementations differ in whether their constructors
require an argument specifying their initial capacity. Initial
capacities are required for hash table based Maps. If none is
given DEFAULT_INITIAL_CAPACITY (from `<T>defs.h') is
used.

Pix-based operations are more fully described in the section
on Pixes. See section Pseudo-indexes

Map d(x); Map d(x, int initial_capacity)

Declare d to be an empty Map. The required argument, x, specifies
the default contents, i.e., the contents of an otherwise
uninitialized location. The second version, specifying
initial capacity is allowed for Maps with an initial capacity
argument.

d.empty()

returns true if d contains no items.

d.length()

returns the number of items in d.

d[k]

returns a reference to the contents of item with key k. If no
such item exists, it is installed with the default contents.
Thus d[k] = x installs x, and x = d[k] retrieves it.

The GetOpt class provides an efficient and structured mechanism for
processing command-line options from an application program. The sample
program fragment below illustrates a typical use of the GetOpt class
for some hypothetical application program:

Unlike the C library version, the libg++ GetOpt class uses its
constructor to initialize class data members containing the argument
count, argument vector, and the option string. This simplifies the
interface for each subsequent call to member function int operator
()(void).

The C version, on the other hand, uses hidden static variables to retain
the option string and argument list values between calls to
getopt. This complicates the getopt interface since the
argument count, argument vector, and option string must be passed as
parameters for each invocation. For the C version, the loop in the
previous example becomes:

while ((option_char = getopt (argc, argv, "dcs:")) != EOF)
// ...

which requires extra overhead to pass the parameters for every call.

Along with the GetOpt constructor and int operator ()(void),
the other relevant elements of class GetOpt are:

char *optarg

Used for communication from operator ()(void) to the caller.
When operator ()(void) finds an option that takes an argument, the
argument value is stored here.

int optind

Index in argv of the next element to be scanned.
This is used for communication to and from the caller
and for communication between successive calls to operator ()(void).
When operator ()(void) returns EOF, this is the index of the
first of the non-option elements that the caller should itself scan.
Otherwise, optind communicates from one call to the next how much
of argv has been scanned so far.

The libg++ version of GetOpt acts like standard UNIX getopt for
the calling routine, but it behaves differently for the user, since it
allows the user to intersperse the options with the other arguments.
As GetOpt works, it permutes the elements of argv so that, when
it is done, all the options precede everything else. Thus all
application programs are extended to handle flexible argument order.

Setting the environment variable _POSIX_OPTION_ORDER disables
permutation. Then the behavior is completely standard.

Programmers who have written C++ classes that they believe to
be of general interest are encourage to write to dl at rocky.oswego.edu.
Contributing code is not difficult. Here are some general guidelines:

FSF must maintain the right to accept or reject potential contributions.
Generally, the only reasons for rejecting contributions are cases where
they duplicate existing or nearly-released code, contain unremovable
specific machine dependencies, or are somehow incompatible with the
rest of the library.

Acceptance of contributions means that the code is accepted for adaptation
into libg++. FSF must reserve the right to make various editorial changes
in code. Very often, this merely entails formatting, maintenance of various
conventions, etc. Contributors are always given authorship credit and shown
the final version for approval.

Contributors must assign their copyright to FSF via a form sent out
upon acceptance. Assigning copyright to FSF ensures that the code
may be freely distributed.

Assistance in providing documentation, test files, and debugging
support is strongly encouraged.

Extensions, comments, and suggested modifications of existing libg++
features are also very welcome.